var arrList = new Array(1, 2, 3, 4, 5)
// 最优
arrList.forEach(function (item) {
    console.log(item)
})

// 中等
for (var i = arrList.length; i; i--) {
    console.log(arrList[i])
}

// 最差
for (var i in arrList) {
    console.log(arrList[i])
}